The present invention relates to a method of making valve sleeves and the actual valve sleeves produced by utilizing this method, particularly reference is made to the construction of valves utilized in two directional hydraulic control systems such as power steering in motorized vehicles.
In recent years, four way valves for two directional control system installations have been of the rotary type. In such rotary type valves, a valve core of a generally cylindrical configuration is rotatably mounted within a valve sleeve. The valve and sleeve each contain a plurality of axially extending mated grooves and contain ports for the controlled flow of hydraulic fluid within the grooves. The actual flow is dependent upon the degree of relative rotation between the valve core and the valve sleeve. Heretofore, the valve sleeves for the rotary valves have had annular grooves on the outer peripheral surface providing for porting of the hydraulic fluid and axial grooves on the interior surface which also provided for the flow of hydraulic fluid. In order to eliminate the defects of a three-piece valve which comprises three pieces of valve sleeve and two rings secured to the ends of the sleeve, and to substantially reduce the cost to manufacture the same, a one-piece valve sleeve has been proposed. In a one piece valve sleeve, the internal slots of the sleeve terminate before reaching the ends of the sleeve. A method of making these valve systems has been shown and discussed in prior art references such as U.S. Pat, No. 3,765,305, by Arthur E. Bishop.
FIGS. 1-6 illustrate prior art power steering valve sleeves. In FIGS. 1 and 2, a valve body 1 is manufactured by a grooving machine. The annular valve sleeve 2 has grooves of circular arc, when viewed in longitudinal cross section, (as shown in FIG. 1) and are rectangular in shape when viewed in transverse cross section (as shown in FIG. 2). The valve body 1 in FIGS. 3 and 4, is manufactured by some type of machining, such as ball end milling, and contains spherical slots 3 on the interior surface of the annular valve sleeve 2. FIGS. 3 and 4 show that the groove 3 is machined into the interior of the valve sleeve 2 and do not extend to both ends of the sleeve. Therefore, in accordance with known groove machining techniques, the size of the cutter for making grooves on the valve sleeve 2 is limited by the size of the interior portion of the valve sleeve 2. Because the cutter must be inserted into the inner portion of the valve sleeve 2, the result is long machining time and nonprecise machined grooves.
In order to overcome the aforementioned disadvantages, a multi-piece valve body 1, such as the one disclosed in FIGS. 5 and 6, has been employed. In FIGS. 5 and 6, the valve body 1 comprises an annular valve sleeve 2 and rings 4. The grooves 3, which allow for flow of hydraulic fluid, extend longitudinally along the valve sleeve 2 and are produced by appropriate machining techniques. The rings 4 are press-fitted into both ends of the sleeve 2 for sealing the entire unit. By utilizing the aforementioned manufacturing process, it is relatively easy to form a variety of differently machined grooves. However, it costs more to produce an increased number of parts and also results in an increase in manufacturing time. Further, if the rings 4 are not properly press-fitted into both ends of the valve sleeve 2, the result is oil leakage. In order to avoid this leakage, strict tolerance standards must be adhered to when manufacturing the annular valve sleeve 2 and the rings 4.